Measuring the average temperature of liquid in storage tanks



Jan. 13, 1953 H. F. TAPP ET AL MEASURING THE AVERAGE TEMPERATURE OFLIQUID IN STORAGE TANKS 4; Sheets-Sheet 1 Filed Avril 4, 1952 50 FEET 34FEET 46 FEET 40 FEET 28 FEET 2| FEET l5 FEET 12 FEET 9 FEET 6 FEET 4FEET M'wfW ATTORNEYS H. F. TAPP ET AL 2,625,043 MEASURING THE AVERAGETEMPERATURE OF LIQUID IN STORAGE TANKS Filed April 4, 1952 4Sheets-Sheet 2 Jan. 13, 1953 I ICE 4 6F- 66 m .1 A A JZZ A'T TO R NEYSJan. 13, 1953 H. F. TAPP ET AL 2,625,043

MEASURING THE AVERAGE TEMPERATURE OF LIQUID IN STORAGE TANKS Filed April4, 1952 4 Sheets-Sheet 5 F'IC3.6

INVENTORS HARRY F. TARP GEORGE D. ROBINSON "r TORNEYS Jan. 13, 1953 H.F. TAPP ET AL 2,625,043

MEASURING THE AVERAGE TEMPERATURE I OF LIQUID IN STORAGE TANKS FiledApril 4, 1952 FIGS? FIGJO FIGJI SEND OF CAM CYCLE ;END OF CAM CYCLE ENDOF CAM CYCLE 4 Sheets-Sheet 4 SW lTCH ACTUATES FIGJZ F'IGJIB F1614 [ENDOF CAM CYCLE END OF CAM CYCLE END OF CAM CYCLE.

SWITCH SW I TCH ACTUATES ACTUATES FIG.I7

END or CAM CYCLE END OF CAM CYCLE END-OF AM CYCLE WITCH ACTUATES oSWITCH o ACTUATES 92 ACTUATES 228 SWITCH ACTUATES ATTORNEYS PatentedJan. 13, 1953 UNITED STATES PATENT OFFICE MEASURING THE AVERAGETEMPERATURE OF LIQUID IN STORAGE TANKS Application April 4, 1952, SerialNo. 280,462

.6 Claims.

liquid is measured and then the volume at 60 Fahr. is calculated.Level-responsive measuring apparatus is available for showing directlyon a meter the level of liquid in the tank. Determination of thetemperature of the liquid, easily and with close accuracy, has been madepossible through electrical apparatus by which the average temperatureof the liquid, when the tank is filled to any one of a plurality ofselected levels, can be indicated directly on a measuring instrument.This temperature measurement apparatus utilizes a temperature-sensitiveresistor, which is immersed in the liquid in the tank and extends fromthe bottom thereof upwardly through and to the surface of the liquid.This resistor is connected in circuit with a suitable measuringinstrument such as a milli-ammeter, and a source of electricity. Changesin temperature of the liquid cause changes in the resistance of theresistor and thus changes of current in the circuit. These changes incurrent are shown on the measuring instrument, which is graduated toread in degrees Fahrenheit. The resistance of the resistor is uniformlydistributed throughout its length and the temperature indicated isaverage temperature over the depth of oil. In practice, a series ofresistors, of equal resistance, extend from the bottom of the tankupwardly and terminate at diiierent levels and these resistors can beselectively connected, one at a time, in circuit with the measuringinstrument. For any given depth of liquid in the tank, the resistorhaving a length nearest to this depth is selected. An operator has toobserve the depth of oil in the tank and then manually move a selectorswitch to the proper position to connect the desired resistor into thecircuit of the measuring instrument.

This invention has for its main object the provision of means forautomatically connecting into the circuit of the measuring instrumentthe proper resistor for any particular depth of liquid that exists inthe tank. I

More particularly, the invention has for an object the provision ofselector switches for the resistors and switch actuators, whicharemovable responsive its-changes in the leyel of liquid in the tank,whereby on a change in level to a predetermined extent, one resistor iscut out of the circuit of the measuring instrument and the next resistorin the series is substantially immediately out into the circuit. Thus,one resistor is always in the measuring circuit and this one is theproper one, that is, the one having a length nearest to the thenexisting depth of liquid in the tank. The operator merely needs toobserve the measuring instrument, which shows at all times the averagetemperature of the liquid in the tank.

This invention will be disclosed with reference to the accompanyingdrawings in which,

Fig. l is a small-scale, fragmentary, sectional elevational view of astorage tank showing an apparatus, embodying the invention, mounted onthe roof of the tank;

Fig. 2 is a similar view showing the apparatus mounted outside and nearthe bottom of the tank;

Fig. 3 is a diagram showing the electrical connections between theselector switches, temperature-sensitive resistors, battery andtemperatureindicating instrument of the apparatus;

Fig. 4 is a sectional plan view taken on the line 4-4 of Fig. 5;

Fig. 5 is an elevational view of the apparatus shown as mounted on topof the storage tank;

Figs. 6 and 7 are sectional views taken on the lines 6-6 and l-'l,respectively, of Fig. 4;

Fig. 8 is a sectional view taken on the line 8--8 of Fig. 7; and

Figs. 9, 10, 11, 12, 13, 14, 15, 16, 1'7 and 18 are views showing thevarious switch-actuating cams.

Referring to these drawings, there is shown in Fig. l a storage tank I,such as is commonly used in the petroleum industry and is usually oflarge diameter, say for example, 90 feet, and of substantial height, sayfor example 50 feet. In this tank is a float 2, secured to one end of atape 3, which passes upwardly in the tank through the gauging hatch 4 onthe roof 4 and into a casing 5, which houses mechanism, to be laterdescribed, for actuating a meter showing the level of liquid in thetank. Also in tank I is a cable 6, which contains the various resistorsused for temperature measurement. This cable extends from the bottom oftank I vertically upwardly and through roof 4, into and through aconduit 1 and into a casing 8, which is attached to casing 5 and housesthe selector switches for the various resistors and the associatedactuating mechanism later to be described.

The resistors are shown diagrammatically at 9 in Fig. 3. Each resistorhas the same resistance (in this example 100 ohms) uniformly distributedthroughout its length. The depth location in the tank of this series ofresistors is indicated in the diagram. The resistors extend upwardlyfrom the bottom of the tank, terminating at different selected levels,as indicated, by way of example by the vertical scale of figures at theleft of the diagram, these figures representing depth in feet in thetank. The resistors may, for example, be wound like coil springs andthen distended to the different lengths required, the resistor for thedepth of 4 feet being most closely wound and the resistor for the depthof 50 feet being wound most openly.

These resistors 9 are adapted to be connected one at a time in anelectrical circuit with a suitable measuring instrument IIl, which maybe of the milli-ammeter type, graduated to read in temperature, as indegrees Fahr, and a suitable power source, such as the battery I I. Thecircuit, as shown, includes a conductor I2, to which the lower terminalsof all the resistors 9 are connected and which is connected to oneterminal of instrument ID; a conductor I3, which connects the otherterminal of this instrument to one terminal of battery II; and aconductor I4, which is connected to the other terminal of the batteryand extends to the selector switches, indicated generally at I5. Eachselector switch includes two pairs of contacts. the contacts of thefirst pair being designated I6 and I! and the contacts of the secondpair being designated l8 and I9. Each switch is biased so that thecontacts l6 and I! are normally connected together and the contacts I8and I9 are normally disconnected, as shown. Actuation of the switchagainst its bias reverses the conditions, causing the contacts I6 and I!to be disconnected and the contacts I8 and I9 to be connected together.Each contact I6 is connected by a conductor 20 to the conductor I4 andthe contact I8 of the last switch of the series (for the highest level)is also connected to wire conductor I4, as by a conductor 2I. The upperterminal of the first resistor 9 of the series (for the lowest level) isconnected by a conductor 22 to the contact I! of the first switch of theseries. The upper terminal of each of the other resistors 9 is connectedby a conductor 23 to the contact I9 of the corresponding switch of theseries. The contact I! of each switch, except the first one of theseries, is connected by a conductor 24 to the contact I8 of thepreceding switch of the series.

With all switches I5 in normal position, which occurs, for example, whenthe depth of the liquid in the tank is below 4 feet, the first resistor9 is connected in the circuit of the measuring instrument In because itsfirst pair of contacts I6 and I] will be connected together, as shown,All other resistors 9 will be disconnected from the circuit because thesecond pair of contacts I8 and I9 of every switch of the series willthen be disconnected. As the liquid rises in the tank to the level 0L4feet, the first switch of the series will be actuated, therebydisconnecting its first pair of contacts I 6 and I I and thusdisconnecting the first resistor 9 of the series from the circuit of themeasuring instrument, and substantially immediately thereafter,connecting its second pair of contacts I8 and I9, and thus causing thesecond resistor 9 of the series to be connected in the circuit of themeasuring instrument through the conductor 24 and the theninterconnected first pair of contacts I6 and II oi the ext witch in theseries. When the liquid in the tank reaches the level of 6 feet, thesecond switch I5 of the series will be actuated, thereby disconnectingits first pair of contacts I6 and I1 and thus disconnecting the secondresistor 9 of the series, and immediately thereafter, connecting itssecond pair of contacts I8 and I9 and thus connecting the third resistor9 into the circuit. Each switch, after having been actuated, is held inactuated position, as the liquid in the tank continues to rise. Thus,the various resistors 9 will be successively connected into the circuitof the measuring instrument I0 and subsequently disconnected until theliquid reaches the level of 46 feet, when the last switch of the seriesis actuated, such switch, when its contacts I8 and 19 are connectedtogether, connecting the last resistor 9 of the series in circuit withthe measuring instrument I0 and leaving it in the circuit until theliquid in the tank falls to the level of 46 feet.

As the liquid falls below this level, the last switch of the series willbe allowed to assume its normal position, disconnecting its second pairof contacts I8 and I9 and thus disconnecting the last resistor 9 of theseries, and connecting togather its first pair of contacts I6 and IT,whereby the resistor 9 for the next lowest level is connected into thecircuit of the measuring instrument through the conductor 24 and thethen interconnected second pair of contacts I8 and I9 of the next lowerswitch in the series. The resistors 9 are thus successively connectedinto the circuit, as the liquid in the tank falls, until the level fallsbelow four feet when the first switch of the series causes the firstresistor of the series to be connected in the circuit of the measuringinstrument andleft in circuit at all levels below 4 feet. The levelsnamed are merely given by way of illustrative example and may,obviously, be varied as desired.

One of the switches I5 is shown in its normal position in Fig. 8. Theparts are mounted in an enclosure of suitable insulating material. Thecontacts of each pair are connected together by a switch member 25,which is of resilient metal and has struck out therefrom two parts 26,forming toggle springs. The inner ends of the springs 26 are engaged onein each of two recesses formed in a bent metal part 21, which is fixedto a push button 28 of insulating material. A spring 25, coiled around arod 30, which is fixed to button 28, acts between a wall of casing I5and a shoulder on the rod, to bias the springs 26 into one extremeposition, in which the member 25 is so positioned as to connect thefirst pair of contacts [6 and I1 and disconnect the second pair ofcontacts I8 and I9. Pressure on button 28 will force the toggle springs26 inwardly through the opening in member 25 until they cross to theother side thereof, whereupon the member 25 is moved with a snap actionfrom the illustrated position to another position, in which the member25 con nects the second pair oi contacts I8 and I9 to' gether. Theswitch, chosen as an illustrative example, is of the type shown in theU. S. patent to Hausler No. 2,332,911, granted October 26, 1943, :towhich reference may be had for a more complete disclosure, if necessaryor desired.

The switch-actuating mechanism is shown in Figs. 6, '7 and 8. Itincludes a shaft 3|, mounted in suitable bearings provided in a frame82, which is located in and fixed to casing 8. This shaft is adapted tobe turned in opposite directions by the rise and fall of float 2 by asuit able transmission including the described ta'pe 3 and other partslater to be described in detail. Fixed to this shaft 3!, preferably in amanner to enable angular adjustment, as indicated, are a plurality ofcams 33 one for each switch l5 and located adjacent the same. Theswitches are mounted side by side in abutment and held together by twolong bolts 35 which clamp them between a wall 34 of frame 32 and anangle iron 36 fixed to frame 32. The button 23 (Fig. 8) of each switchis adapted to be pressed inwardly by its cam, acting through a camfollower 3'! on the free end of a rocker arm 33, which is connected tothe switch casing [5 for swinging movement by means of a fiat spring 39.The periphery of each cam 33 is divided into a low dwell portion 46 ahigh dwell portion 4! and connecting transition portions 52 and 43. Whena follower 37 rides on the low dwell portion 49 of its cam 33, thebutton 28 of its switch it occupies its outer position and the two pairsof contacts IS, IT and 13, I9 assume the described normal positions, towhich they are biased. When the follower 37 is engaged by the part 42 ofits cam, the button 28 is moved inwardly to actuate the switch [5 andreverse the positions of the two pairs of contacts, as described. Whenthe follower 3'! rides on the high dwell portion ll of the cam, thebutton 28 of its switch is maintained in its inwardly-pressed oractuated position.

The cams 33 are shown one in each of Figs. 9 to 18 and in the order inwhich they occur in the series. The cams are generally alike and differonly in the angular extent of the low dwell portions 49, whichsuccessively increase from the first to the last cam of the series, andin the angular extent of the high dwell portions H which successivelydecrease from the first to the last cam of the series. The end of thehigh dwell portion ll of each cam 33 has the same angular position onshaft 3!. As viewed in Figs. 9 to 18, the shaft 3! is adapted to beturned clockwise and counterclockwise by the rise and fall,respectively, of the float 2 in tank i. The cams are shown in thepositions, which they occupy when there is two feet of liquid in tank I.This is usually the lowest level to which liquid can be drawn out of thetank. The cam shaft 3!, as herein shown, is adapted to be turned 6 bythe travel of float 2 through the distance of one foot. Each camfollower 3'! rides on the low dwell portion it of its cam. As the camsturn clockwise 12, the rise 42 of the first cam of the series, shown inFig. 9, will have engaged and moved its follower 31 to actuate the firstswitch it of the series. On another 12 movement of the earns, the secondcam of the series, shown in Fig. 10, will have moved its follower 3'3 toactuate its switch and so on, the various switches of the series beingsuccessively actuated, and each being held in actuated position by thehigh dwell portion it! of its cam until the last switch it of the seriesis actuated, when the liquid has a depth of 48 feet. The float 2 cancontinue to rise to the top of the tank I, the dwell portion 41 of thelast cam 33 shown in Fig. 18, being of sufficient extent for thepurpose. As the liquid is drawn out of tank I, the shaft 3| will beturned counterclockwise and the came 33 will successively allow theswitches I5 to move back to their nor mal positions, at thevarious'levels indicated.

The transmission between the float 2 and cam shaft 3| may, of course,vary as desired, the only necessary condition being that the cam 6 shaftbe turned back and forth by, and in proportion to, the rise and fall ofthe float and to an adequate extent. In the present example, the camshaft Si is driven from a level-indicating mechanism actuated by float2. Referring to Fig. 5, which shows the casing 5 mounted on top of thegauging hatch 4' on the roof 4 of tank l, the tape 3 passes verticallyupward in the hollow casing 5, part way around a sprocket 4A, which haspins 45 to engage in perforations in tape 3, and then horizontally tothe right to a drum 45 on which the tape is wound. The sprocket id isfixed to one end of a shaft ll, mounted, as indicated in Fig. 4, insuitable bearings provided in the casing 5. Fixed to the shaft 38 of thedrum 46 is a second drum 48 and adjacent thereto is a similar drum 50,fixed to'a shaft iii. The shafts 4B and 5| at one end are supported in awall of casing 5 and at their other ends in a frame 52, secured as shownin Fig. 5 to casing 5. Covers 53 and 53, secured as indicated to casing5, provide for access to the compartments in which the sprocket M andthe-drums t6, "t9 and 5B are respectively located. The cover 53 isomitted in Fig. 5, the better to show interior mechanism. The drums 49and 5!] are connected by a spring 5i. One end of this spring is fixed toone drum and the other end to the other drum. As the spring un Windsfrom one drum, it winds upon the other. It exerts a constant torquetending to turn the large drum it in a clockwise direction and thusbalance the weight of the float. In the present example, the spring 5 1is of a special type, which is known by the trade mark Neg-A-Tor, andprovides constant torque as it winds and unwinds.

The shaft i'i (Fig. 4) has fixed on its inner end a crank 55, the pin 58of which is engaged in a slot in another crank 51, which is fixed to ashaft 55. The latter drives the movable element of a potentiometer, thestationary element'of which is shown at 59, suitably fixed to a plateso, secured in the upper part of casing 8 and located above the cams andthe selector switches. Shaft 58 extends through plate 69 and carries apinion 6| which drives a gear 62, which, as shown in Fig. 6, is fixed toa shaft 53. The latter carries the movable element of a secondpotentiometer, the stationary element of which is shown at 64 fixed toplate til. The shaft 63 has fixed thereto a worm 65 (Fig. 7) whichdrives a worm gear 66, fixed to cam shaft 3!. As herein shown, thesprocket fi l is turned one revolution by a one foot movement of tape 3.Shafts 5? and 63 are geared 1 to 6 so that one revolution of the formercauses one sixth revolution of the latter. Ten revolutions of worm Eproduce one revolution of gear 66 and thus of shaft 31. Thus, a movementof float 2 through a distance of one foot will produce one sixtieth of arevolution of shaft 3! or an angular movement thereof of 6 degrees.

The potentiometers 59 and 54 are adapted to be connected in an electriccircuit with a suitable measuring instrument to vary the current in suchcircuit and these variations are indicated on the instrument in feet andinches, the potentiometer 55 controlling the inch scale and thepotentiometer 5t controlling the foot scale. This levelindicatingapparatus is not completely shown herein because an understanding of itsconstruction and operation is not essential to an understanding of thepresent invention' Y There is also shown in Figs; 4 a'nd6 another formerlevel indicator at 61. This indicator is a register of the number wheeltype, the indications of which in feet and inches are displayed througha window 68 in casing 23. The register 61 is driven by bevel gears 59(Fig. 4) from a shaft I0,- Which is connected by a gear train II toshaft 58. The register 61 and gear train H, gears 69 and shaft ID aresupported in a frame I2, fixed as indicated in Fig. 4 to the casing 8.The latter has a removable cover 13 which allows access to the mechanismmounted therein.

The mechanism described need not necessarily be mounted on the roof ofthe storage tank as shown in Fig. 1. An alternative mounting is shown inFig. 2, in which casings and 8', respectively corresponding to thedescribed casings 5 and 8 and containing the same mechanisms, aremounted on a concrete base 14 near the ground. The casing 5 is extendedhorizontally to the right far enough to receive the second sprocketwheel "I5. The tape 3 in leaving the sprocket 44 passes down and undersprocket I5 and thence upward through a vertical pipe I6 to a sprocketI1 and thence horizontally through a pipe I8 to a sprocket I8 and thencevertically downward through ap'ipe 8|] into the storage tank. The resisto'r cable 6 extends through a conduit 8| to casing 8. The conduit BIand pipe I6 are suitably supported from the shell of the storage tank,as indicated.

Inoperation, the float 2, as it rises and falls in the storage tank Iwith changes in level of the liquid therein, causes the cam shaft 3I tobe moved back and forth, or clock-wise and counter-'- clockwise,respectively, as viewed in Figs. 9 to 18, to control the series ofswitches I5. nt example, because ofthe speed reduction mechanisminterposed between the float 2 and shaft 3|, a movement or one foot ofthe float causes a movement of- 6 ofthe cam shaft, which has an angularrange of 390 for the entire depth of 50 feet of tank 1'. Therefore, theshaft 3I will move very slowly, and it is necessary that thecontact-connecting member 25 of each switch I5 be actuated from oneextreme position to the other by suitable snap-acting means, such as thetoggle springs 26, when permitted by its controlling cam 33 onshaft 3I.-The spring 29 of each switch, as the biasing means, tends to hold theswitch member 25 in the first of its two extreme positions, in which thecontacts I6 and I! of the first pair are connected and the contacts I8and I9 of the second pair are disconnected. When the transition riseportion 42 of a cam 33 engages its follower 31,. the" snap-acting meansis moved against the biasing means into its second position,

in which the contacts I6 and I! of the first pair are disconnected andthe contacts I8 and I9 of the second pair are connected. This occurs ateach of a plurality of predetermined angular positions of shaft 3'I,corresponding to a plurality of predetermined levels of liquid in tankI. Each switch, after havingbeen thus actuated, is held in actuatedposition by the high dwell port on II of its cam, if the level of liquidin tank I remains at or rises above the predetermined level. If thelevel of liquid falls, the cam 3| turns in the oppo- Site direction(counterclockwise as viewed in Figs. 9 to 18) and as its follower 31rides down the transition portion 42 of its cam 33 onto the low dwellportion 4'] thereof, the biasing means 29 is released and allowed tomove the snap-acting means 26 to its first position, thereby movingmember 25' todisconnect the contacts 18 and I9 of the second pair andthen connect the contacts I8 and I1 of the first pair. Figs. 9 through18 re- In the pres spectively showthe cams for the first through thetenth switch of the series and indicate the various angular positions atwhich the switches will be actuated and the various angular rangesduring which they are actuated.

Referring to the diagram of Fig. 3, it will be seen that the circuit foreach resistor 9, except the first and last ones of the series, which arenot frequently used, includes in series two pairs of contacts, one pairin one switch of the series and another pair in the next switch of theseries. No more than two pairs of contacts are ever included in thecircuit of the measuring instrument. Thus, the resistance due to theselector switches is maintained as nearly uniform as possible, the onlyexception being in the circuits of the end resistors of the series whichare less liable to be used.

The Fig. 3 diagram shows the switches as positioned when the level ofliquid is below four feet. Each switch is in its normal position. Thus,the first pair of contacts I6 and I I of each switch are connected andthe second pair of contacts I8 and I9 of each switch are disconnected.The only resistor 9 then in the circuit of the measurin instrument It isthe first one of the series. All other resistors of the series aredisconnected from such circuit by the then disconnected second pair ofcontacts I8 and I9 of each switch. When the liquid in tank I rises tothe level of four feet, the first switch I5 of the series will beactuated by the part 42 of its cam 33, causing the first pair ofcontacts I6 and l I to be disconnected, thus disconnecting the firstresistor 9 of the series from the circuit of the measuring instrumentI0, and its second pair of contacts I8 and I9 to be connected, thusconnecting the second resistor 9 of the series into the circuit of themeasuring instrument. When the level of liquid in tank I rises to 6feet, the second switch I5 of the series will be actuated, causing thesecond resistor 9 of the series to be disconnected and the thirdresistor of the series to be connected to the circuit of the measuringinstrument. As the level of liquid in tank I continues to rise, theother switches will be actuated successively in order at the differentlevels indicated and other resistors of the series connected intothecircuit of the measuring instrument. As the level of liquid in tank Ifalls, the various cams 33 will release their respective switches IS inorder and this will cause, at various predetermined positions named, thedisconnection of a higher level resistor from, and the connection of theresistor for the next lower level to be connected to, the circuit of themeasuring instrument.

The switch-actuating means described may obviously be reversed, ifdesired. That is the cams may turn in a direction opposite to thatindicated in Fig. 8; the switches being held by the high dwells M of thecame in normal positions and successively actuated by their rollersriding down the portions 42 onto the low dwell portions of the cams. Theleft hand pair of contacts in Fig. 8 would then become the contacts I8and I1 of the diagram of Fig. 3 and the right hand pair of contacts inFig. 8 would then become the contacts I8 and I9 of the diagram. In thecam charts the position marked End of the cycle would become the startof the cycle, and the angular extent of the high dwell would be the sameas the illustrated angular extent of the low" dwell and v'ice versa, sothat the switches can be successfully actuated at the same angularpositions illustrated. The operation would not be changed by thedescribed reversal of parts of the actuating mechanism.

It will be clear that with the described apparatus, whatever the levelof liquid in tank i may be, there will always be connected in thecircuit of the measuring instrument It one resistor 9 and that resistorwill be the proper one for the particular depth of liquid in tank I.That is, the active resistor in the circuit will be one having a lengthapproximating the then existing depth of liquid in the tank. As thelevel changes to a sufficient degree, the resistor in the circuit isautomatically changed. Thus, it is merely necessary to read themeasuring instrument It which shows at all times within close limits theaverage temperature of the liquid in the storage tank.

What is claimed is:

1. In apparatus for measuring the average temperature of liquid in astorage tank, of the type wherein a series of resistors havingequalresistance extend upwardly from the bottom of the tank and terminate atdifierent levels, the resistance of each resistor being uniformlydistributed over its length, and wherein such resistors are adapted tobe selectively connected one at a time in an electrical circuit, whichincludes a measuring instrument. responsive to changes of resistance inthe circuit and which is adapted for connection to a source ofelectricity; an element movable in response to and proportionately withchanges in level of the liquid in said tank, and switching meansactuated by movement of said element for connecting said resistors oneat a time in said circuit and operable when moved into each of aplurality of predetermined positions, to disconnect one resistor of theseries from said circuit and connect into the latter a next succeedingresistor of the series.

2. In apparatus for measuring the average emperature of liquid in astorage tank, of the type wherein a series of resistors having equalresistance extend upwardly from the bottom of the tank and terminate atdifferent levels, the resistance of each resistor being uniformlydistributed over its length, and wherein such resistors are adapted tobe selectively connected one at a time in an electrical circuit, whichincludes a measuring instrument responsive to changes of resistance inthe circuit and which is adapted for connection to a source ofelectricity; an element movable in response to and proportionately withchanges in level of the liquid in said tank, a series of switchessuccessively actuated by said element one at each of a plurality ofpredetermined positions of said element; each switch including a firstand a second pair of contacts initially held connected and disconnectedrespectively, said element actuating each switch to disconnect thecontacts of the first pair and then connect the contacts of the secondpair, each resistor except the end ones of the series being controlledby the second pair of contacts of one switch and the first pair ofcontacts of a next adjacent switch in the series, whereby as each switchis actuated by said element to connect another resistor of the series itdisconnects the preceding resistor of the series.

3. In apparatus for measuring the average temperature of liquid in astorage tank, of the type wherein a series of resistors having equalresistance extend upwardly from the bottom of the tank and terminate atdifierent levels, the resistance of each resistor being uniformly dis-10 tributed over its length, and wherein such resistors are adapted tobe selectively connected one at a time in an electrical circuit, whichincludes in series a conductor connected to one terminal of eachresistor, a measuring instrument responsive to changes of resistance inthe circuit and a second conductor, said circuit being adapted forconnection to a source of electricity; an element movable in response toand proportionately with changes in level' of the liquid in said tank, aseries of switches successively actuated by said element one at each ofa plurality of predetermined positions of said element; each switchincluding a first and a second pair of contacts initially held connectedand disconnected respectively, said element actuating each switch todisconnect the contacts of'th'e first pair' and then connect thecontacts of the second pair, said second conductor being connected toone contact of the first pair of each switch, and other conductors onefor each resistor and each connecting the other terminal of its resistorto one contact of the second pair of a switch, and a conductorconnecting the other contact of the first pair of each switch except thefirst switch of the series to the other contact of the second pair ofthe preceding switch of the series, the circuit for each resistor thusincluding in series the second pair of contacts of one switchand thefirstpair of contacts of the second switch, whereby as each switch isactuated to connect another resistor of the series in the circuit ofsaid instrument, it disconnects the preceding resistor of the series.

4. Switch actuating mechanism comprising, a shaft adapted for connectionto a level-responsive element of a liquid storage tank and to be movedback and forth by the rise and fall of liquid therein, a plurality ofcams on said shaft, each having low and high dwell portions and atransition portion interconnecting the dwell portions, a plurality ofswitches mounted one adjacent each cam, each switch having a first and asecond pair of contacts, snap-acting means movable from a firstposition, in which the contacts of the first pair are connected and thecontacts of the second pair are disconnected, to a second position, inwhich the contacts of the first pair are disconnected and the contactsof the second pair are connected, and a follower riding on each cam andconnected to the snap-acting means for moving the same into its secondposition, said follower being moved by said transition portion of thecam to actuate the snap-acting means into its second position and beingheld in the position to which it is moved by one dwell portion of thecam to hold the snap-acting means in its second position, the transitionportions of the several cams being located in diiferent angularpositions on said shaft, said last-named dwell portion increasing inangular extent from the first cam to the last cam of the series.

5. Switch mechanism, comprising, a plurality of switches; each switchhaving a first and a second pair of contacts, a member movable from afirst extreme position in which it connects the contacts of the firstpair and disconnects the con tacts of the second pair to a secondextreme position in which it disconnects the contacts of the first pairand connects the contacts of the second pair, snap-acting means formoving the member from one said position to another, and meanscontrolling the snap-acting means and tending to hold the member in saidfirst position; a conductor adapted for connection to the circuit of ameasuring instrument and a power source and connected to one'contact ofthe first pair 'of eachswitch, a'plurality of conductors one for eachswitch and each connected to one contact. oi the second pair of itsswitch and adapted for connectionon'e to each of a plurality of reistorsto be connected in said circuit, a condoct r onnecting the other.contact of the first pair of each switch to. the other contact of thsecond pair. i e next adjac nt Switch of. th? e ies, said. mea sv beingmovable to. actuate. the switche o e at a time to. move its member fromeeid ir t to aki econd. position.

S itQh m chanism, comp i n a plurality o switch s; e ch. switch havin airst and a ec nd. air. o contac s, a; m mber moyab e rom fire; e treme,noe ticn' n which i con ect t e epnteet o t e. firet pai and ci e chnets the. c neete Qi the $9991.19 air o a ecep ex reme 9- .i9 wh ch. itdieeenneete t e. c ntact of th firet Pei? a i the.9 ;.1tect v of th secoe. ve eeeer eiine a, theft; mov n t e 1.11%). e; eet 95 ee q e 9 epet erand me ne eet 'elli e. enepe ee. were nd endin le the m me in are. 3 1 1neei hn: e .9. 1- 't r ade -e2 for eene ctien t the. ci cuit of a measing e i ment a l?! P9279! we e: 9 i 'd more taet 9 the fir t neire e chtc y "9f e nel 'qte e e o each switch and each connected. to onecontactof the SBGO'Iid pen or. itsfswitehjaji 'd aqa sg q foii connection oneto each ot a. plurality of resistors to be connected insaid' circuit; a.conductor connecting the'other contact otthe first pair. of each switchtothe other contact 'of the second pair of the next adjacent switch 01the. series, said controlling means. adapted for connection to thelevel-responsive element of. a liquid storaee tank a d tube moved backand forth by the rise and fall. ofl quid therein. the movement of saidcontrolling means in one. direction into each of; vari- 011s pretermined positions actuating the snapactin means of a, switch to. moveits member into sa d. econd nositione d in. the. other d rectionactuating the snap-actin means oi a switch. to move ts-m mber nto said frst DDSition.

" E- TAPP- GEORGE D, R BINSON- BEEEREN ES ITED The following referencesare of record in the file of this patent NI -e1 re-Tee. PA TI

